The present invention relates to a both-sided image forming method of an electro photographic system by which two-component developer including resin distribution type carrier of a phenol-formaldehyde resin is used.
Recently, in the electro photographic system image forming method, by using so called electronic RDH (Recirculating Document Handler), electronically both-side printing is conducted. The both-side printing by this electronic RDH is different from the system by which the both-side printing is conducted by the conventional analogue copier, the print printed on one surface of a recording sheet (an image formation substrate) is not stacked in an intermediate tray, and can continuously print directly on the other surface of the recording sheet. That is, based on the image signal converted into the digital signal, the first electrostatic latent image is formed on the electrostatic latent image carrier, and based on this electronic latent image, the toner image is formed, and after this toner image is transferred onto one surface of the recording sheet and fixing processing is conducted, the recording sheet is not stacked in an intermediate tray, when the toner image formed based on the second electrostatic latent image formed on the electrostatic latent image carrier is directly transferred onto the other surface of this recording sheet and fixing processed, the both-side printing is conducted.
In the both-sided surface image forming method by using this electronic RDH, when the fixing processing is conducted by the heating system, the high temperature recording sheet holding the heat by the fixing processing circulates in the device, and the temperature in the device rises by the result that the recording sheet itself is effected by the influence of the holding heat.
On the on hand, as the carrier in two-component developer, the resin distribution type carrier in which in the phenol-formaldehyde resin, the magnetic fine powder is distributed is light weight, further because hardness is high, it is usable as the carrier having the high durability (for example, refer to the Japanese Patent O.P.I. Publication (Tokkai) No. 2001-201893.). Because such a carrier is manufactured by the polymerization method, the shape close to the true ball or the uniformity of the surface is obtained, and the high electrostatic holding property is obtained. Further, in the phenol-formaldehyde resin forming the carrier, monomer component (formaldehyde) remains, and this monomer component is the low molecular weight, and has the polar group, and when this monomer component exists, the high electrostatic charge giving property of the carrier to the toner can be obtained.
However, when two-component developer using the carrier including the phenol-formaldehyde resin is applied to the both-sided surface image forming method by the electronic RDH, although the carrier itself has no generation of surface contamination, there is a problem that the image density is lowered or the toner scattering is generated.